This invention is related to a two way over-running clutch, preferably for use in automotive differential applications. More specifically, the present invention relates to a two-way over-running clutch assembly of a roller/ramp variety which can be controlled for selectively locking up an automotive differential assembly.
This invention is related to devices and methods as described in United States Provisional Application No.: 60/223,882, filed Aug. 8, 2000, and United States Provisional Application No.: 60/258,383, filed Dec. 27, 2000, all of which are commonly assigned.
Differential assemblies are used in motor vehicles to allow the wheels to turn at different rotational speeds while still providing power to the wheels. Various types of differential assemblies are used in motor vehicles to redirect the transfer of power to the driving axles.
In a standard differential, as a vehicle turns, power continues to be provided through pinion and ring gears to the differential housing. As the inner and outer wheels describe different circles or radii, side gears attached to axle shafts are allowed to turn at different speeds by the motion of intermediate spider gears. As long traction is maintained between the drive wheels and the road service, the power is properly distributed to the wheels through the differential assembly. However, when traction is reduced or lost altogether, a standard differential assembly will spin uselessly, providing little tractive power to the wheels. For instance, if one tire is on ice or some other slippery service while the other is on dry pavement, slip will occur at the low friction side and all the power through the differential assembly will be sent to the slipping tire. No power will be delivered to the wheel on the dry pavement and the vehicle will not be powered forward or backward. Therefore, there is a need to lock the axle halves together in certain situations.
A differential assembly design that is used to overcome the shortcomings of the standard differential assembly is known as the locking differential. A locking differential typically engages a xe2x80x9cdogxe2x80x9d clutch or an axial gear set to lock the two axle halves together. Unfortunately, locking differentials cannot be engaged xe2x80x9con-the-flyxe2x80x9d because any relative motion between the gear teeth would result in severe mechanical damage. It would be desirable to selectively lock the differential assembly instantaneously during xe2x80x9con-the-flyxe2x80x9d operation.
It is known in the art to selectively lock other drivetrain components using roller/ramp clutch assemblies. For example, the two-way over-running clutch assembly described in U.S. Pat. No. 5,927,456, assigned to NTN Corporation, and hereby incorporated by reference, describes a clutch assembly of a roller ramp variety and the mechanism by which the rollers are retained and biased in the assembly. In addition, the rotation transmission device described in U.S. Pat. No. 5,924,510, also assigned to NTN Corporation, and hereby incorporated by reference, discloses a device which includes a clutch assembly mounted in the transfer case of a four-wheel drive vehicle that can selectively transmit a driving force.
It would be desirable to provide this technology for use with differential assemblies to selectively lock the two axle halves together during xe2x80x9con-the-flyxe2x80x9d operation.
A primary object of this invention is therefore to provide a two-way over-running clutch mechanism, such as that disclosed in U.S. Pat. No. 5,927,456 or U.S. Pat. No. 5,924,510, installed in the differential assembly of a motor vehicle which when energized will lock together a side gear or drive axle and the differential housing so that no relative rotation can occur between the two drive wheels. This system will provide on-demand traction and can be controlled by an electromagnetic trigger clutch or by hydraulic, pneumatic or other means.
Another object of the present invention is to provide a differential assembly which can be selectively locked together instantaneously during xe2x80x9con-the-flyxe2x80x9d operation.
In accordance with an aspect of the present invention an over-running clutch assembly comprises an outer race having a cylindrical inner surface and being rotatable about an axis and a case end enclosing a first end of the outer race, an inner race having a segmented (flat or slightly concave) outer surface coaxial with the cylindrical inner surface and defining a gap therebetween. The inner race is rotatable about the axis with rotational movement relative to the outer race. A plurality of ramp surfaces formed at spaced apart locations on the outer surface define a plurality of cammed surfaces on the outer surface of the inner race. A plurality of rollers are positioned between the outer race and the inner race with one of the rollers being located centrally within each of the cammed surfaces and each of the rollers having a diameter less than the gap between the center of the cammed surface on the inner race and the cylindrical inner surface of the outer race. A retainer interconnects all of the rollers and causes the rollers to circumferentially move in unison with one another. The retainer is rotatable about the axis with limited relative rotation with respect to the inner race. A first biasing element is supported on the retainer to radially bias the retainer position relative to the inner race such that each of the rollers is held in the center of the flat cammed surfaces on the inner race. An actuation disk is connected to the retainer by a means which allows some axial movement of the activation disk with respect to the retainer toward the case end. The preferred method would include a retainer tab extending axially from one end of the retainer and a notch which is adapted to engage the retainer tab thereby preventing circumferential or relative rotational motion of the actuation disk relative to the retainer and allowing axial motion of the actuation disk relative to the retainer. A second biasing element is disposed between the actuation disk and the inner axial surface of the case end to bias the actuation disk away from the case end.
The clutch assembly includes an actuator to selectively overcome the second biasing element to force the actuation disk into contact with the case end, wherein rotation of the outer race and case end with respect to said inner race is frictionally transferred to the actuation disk and the retainer, overcoming the first biasing element, thereby moving the rollers along the ramp surfaces to a position where the rollers engage and wedge between the inner and outer races to prevent relative rotation between the inner and outer races.